1. Field of the Invention
The present invention relates to a power control device and method for a mobile communication system, and more particularly, to a power control device and method of controlling a gain of pilot signals and a gain of traffic signals in a different manner, respectively.
2. Description of the Related Art
It is common to employ code division multiple access (CDMA) technology for a mobile communication system. The CDMA mobile communication system employs power control for forward link and reverse link. In the CDMA mobile communication system, a receiver of a mobile station receives pilot signals via a pilot channel, which is among the channels used for receiving frame signals transmitted from a transmitter of a base station, and measures the strength of the received pilot signals. The receiver generates a power control signal based on the strength of the pilot signals and sends the generated power control signal back to the transmitter. Concretely, the receiver compares the strength of the pilot channel signal with a reference value (or threshold) for the power control. If the strength of the pilot channel signal is lower than the reference value, the receiver sends a power-up signal; otherwise, the receiver sends a power-down signal back to the transmitter.
In the case where the channel surroundings are poor during communication with a base station (a first base station) at a first frequency having a specific frequency range, a mobile station searches for another base station (a second base station) with better channel surroundings that uses a second frequency having a different frequency. If the searching result indicates that the signal strength of the second base station is better than that of the first base station, the mobile station performs a hard handoff (an inter-frequency hard handoff) from the first base station to the second base station. The searching process, a preliminary step that the mobile station performs for a hard handoff, will be described in the following. The mobile station changes the first frequency as a communication frequency to the second frequency in order to search the second base station for a predetermined time period. Then the mobile station receives the pilot signals from the second base station at the second frequency before returning to the original first frequency. In some cases, transmission of the traffic signals in the mobile station may be discontinued to the presently connected first base station during an interval where the pilot signals are received from the second base station at the new second frequency.
As stated above, the traffic signals are punctured during an interval where the pilot signals are received at another frequency, resulting in a loss of energy. In order to compensate for the loss of energy, the transmitter increases power of the non-punctured frame signals. This is further detailed below.
Generally, the amplitude of a signal denotes a gain or power. The power is the square of a gain. Hereinafter, it will be given to you uniformly as a gain regarding the amplitude of the signal.
FIG. 1 illustrates a device for controlling gain during transmission of a punctured frame on a reverse link, in accordance with the related art, in which signals are composed of pilot signals and traffic signals. Referring to FIG. 1, a controller 100 controls the entire operation of a receiver. The controller 100 controls a pilot signal generator 110, a traffic signal generator 120, and a first signal controller 180 according to signalling information, e.g., data rate, puncturing start time and puncturing interval, etc., received from an upper layer. Under the control of the controller 100, the pilot signal generator 110 generates pilot signals and outputs the generated pilot signals to a first gain controller 130. Upon receipt of the pilot signals, the first gain controller 130 controls the gain of the pilot signals using a predetermined gain GP and outputs the gain controlled pilot signals to a signal combiner 150. Similarly, the traffic signal generator 120, under the control of the controller 100, generates traffic signals and outputs the generated traffic signals to a second gain controller 140. Upon receipt of the traffic signals, the second gain controller 140 controls the gain of the traffic signals using a predetermined gain GT and outputs the gain controlled traffic signals to the signal combiner 150. A ratio of the pilot gain from the first gain controller 130 to the traffic gain from the second gain controller 140 is set to a predetermined value. The signal combiner 150 combines the traffic signals and the pilot signals received from the first and second gain controllers 130 and 140, respectively.
Also, the controller 100 calculates a compensation gain for a puncturing interval based on information concerning the puncturing start time and puncturing interval received from the upper layer. After completion of the calculation, the controller 100 outputs the puncturing interval and the calculated compensation gain to the first signal controller 180. Then, the first signal controller 180 outputs the received compensation gain to a multiplier 170 during the puncturing interval.
The multiplier 170 multiplies the combined signals of the pilot signals and the traffic signals as, outputted from the signal combiner 150, by the compensation gain, and outputs the result to a second signal controller 160. The second signal controller 160 receives the compensated pilot signals and traffic signals and adjusts power control according to the condition of the transmission channels. If a mobile station searches for another base station having a different frequency, puncturing occurs after signal controlling is performed by the second signal controller 160. Thus, both the pilot signals and the traffic signals are punctured during the same time interval.
FIG. 2 illustrates gain distribution for a punctured frame. When a frame is not punctured, the non-punctured frame will be transmitted with a constant gain GA without a gain loss over the entire frame duration A. However, when the frame is punctured causing a gain loss GA at a punctured duration AP, the non-punctured durations B increase in gain by GB to compensate for the gain loss GA at the punctured duration Ap. In conclusion, the total gain for the punctured frame outputted from the multiplier 170 is GTotal=GA+GB.
In the case where the punctured frame is transmitted in the above gain control method, the transmission gain for the non-punctured portion is increased consequently causing an increase in the transmission gain for the pilot signals, which results in the estimated gain of the pilot channel being higher than a reference value during most time intervals. Thus, the gain control signal is generated as a gain-down signal. This gain control method however cannot provide maintenance of a reception performance at the receiver, since the reception performance for decoding the punctured frame is maintained only with a continuous increase in the gain by that time interval for decoding the punctured traffic frame. To avoid such an impairment, the transmitter performs gain control ignoring the gain-down signal among the gain control signals fed back from the receiver, after having decreased during fading and having then recovered therefrom.
As described above, the transmitter ignores the gain-down signal among the gain control signals fed back from the receiver such that only the gain-up signal is activated with the gain-down signal inactivated after having recovered from a deep fading, resulting in a waste of gain.
Furthermore, another problem arises in that data transmission with high gain causes an increase in interference on the reverse link and reduces the capacity of the reverse link.
It is, therefore, an object of the present invention to provide a device and method for controlling gain during the transmission of a punctured frame, in which the punctured traffic data frame can be gain controlled under a gain-up/down signal in the same manner as a non-punctured traffic data frame by controlling the gain for the gain of the punctured traffic data frame only, and without compensating the gain for pilot signals.
In accordance with an aspect of the present invention, a code division multiple access (CDMA) mobile communication system for controlling gain for a traffic signal of one frame is provided, including: a signal generator for generating a pilot signal and the traffic signal on the frame basis; a gain compensator for compensating the gain of the traffic signal according to a punctured length of a punctured frame among the frames; and a signal combiner for combining the gain-compensated traffic signal and the pilot signal generated from the signal generator.
In accordance with another aspect of the present invention, a gain control method in transmission of a punctured frame in a mobile communication system is provided, including the steps of: determining whether an input frame during a hard handoff is punctured or not; when the frame is punctured, determining whether information is received regarding a data rate of the frame and a punctured length; when the information is received, calculating a compensation gain from the data rate and the punctured length; determining whether a frame boundary is detected or not; and when the frame boundary is detected, generating the compensation gain to a multiplier to compensate a loss of gain for traffic signals.